Napalm girl is a powerful photo. So are photos of Aushwitz. So too are photos of trench warfare. Saddam Hussein's hanging is historically important, as are all the images of children killed in Aleppo, or drowned families washing up on shores in Italy.
That doesn't mean we need all these things on Facebook.
I'm sensitive to censorship, and Facebook is a powerful and important platform for sharing, but I'm not prepared to say every photo of historical significance must necessarily be allowed.